The tread portion generates heat during rotation of the tire with a load applied thereon and is subjected to high temperature, which leads to various failures such as heat separation. Therefore, in order to lower the temperature of the tread portion, it is necessary to reduce the heat generation or to promote heat dissipation.
Conventionally, in order to lower the temperature of the tread portion, there has been employed a method of forming grooves in the tread portion so as to remove tread rubber that serves as a heat source while increasing a surface area of the tread portion such that the heat dissipation is enhanced (see, for example, Patent Literature 1).
Further, in order to enhance heat dissipation effect in the tread portion, there has also been known a technology in which, with respect to a narrow groove extending in the width direction, small grooves extending in a direction intersecting the longitudinal direction of the narrow groove are provided, so as to disturb the flow of air within the narrow grooves (see, for example, Patent Literature 2).